1. Field of the Invention
The present invention relates to power generation equipment, and more specifically to dc to ac power inversion circuitry.
2. Description of the Related Art
Because of its versatility in numerous situations, alternating current (AC) power has for many years been the primary type of power utilized in operating electrical equipment. Such power is generally produced by means of generators which are in turn powered by fossil fuels, hydroelectric, and the like sources. Many AC electrical power needs are met by the utility company output provided by the aforementioned generators.
However, AC power may also be produced from a direct current (DC) source by voltage, phase and frequency conversion which is most generally accomplished by use of transformers and/or motor-generators. DC power is most commonly utilized as a source for AC power in situations where it is not possible or feasible to interconnect the AC load to a conventional source of AC power, such as an AC power outlet located remote from the area of service by an electric utility.
For example, it would be desirable to have the capability to operate computer equipment, radio equipment, and the like in a mobile environment away from the utility mains and without the need to lug around cumbersome plug-in DC power adaptor cords. Additionally, with the ever increasing popularity of electric and hybrid-electric powered cars, there exists a burgeoning need to have alternative ways of producing AC power from a DC source.
In known systems, conversion of DC power to AC has traditionally required rotating devices including such things as rotors, bearings, stators, armatures, commutators, slip rings, brushes, shafts, and the like. These systems are far too bulky to incorporate in today's modern and light weight electrical vehicles.
Over the past 3 decades, the aforementioned rotating power conversion equipment has been supplanted by solid state switching equipment, some even being transformerless. Often these solid state switching schemes for generating AC from DC involve complex circuitry requiring intricate oscillator, heat dissipation, and feedback control designs. The aforementioned complex circuitry increases failure rates. For ordinary civilian usage, the failure rates of such solid state circuitry may be an acceptable risk. However, when power inversion is required under harsh environmental conditions, such as extreme heat, extreme dust, radiological bombardment, and the like, it would be desirable to have and employ a DC to AC power inversion apparatus that would be virtually impervious to the aforementioned harsh environmental conditions.
Moreover, it would be desirable to have a DC to AC power inversion apparatus that could utilize excess AC power to supplement energy received from the DC sources. However, to supplement the DC energy source requires a power conversion of the excess AC power back into DC. Thus it would additionally be desirable to have a DC to AC power inversion apparatus that could efficiently re-convert the excess power to charge supplemental batteries, for example.
With respect to a waveform of a DC to AC power generator, it would be advantageous to provide a square wave form AC signal, as opposed to a sine wave which generally has an RMS value of 0.707 times the wave's peak voltage. For example, Japanese Patent 4-91663, dated March, 1992 describes a control circuit that provides a square wave form oscillator that derives an output signal from the AC mains. It should be noted that AC mains is required to make the aforementioned oscillator function, thus, unlike the present invention, Patent 4-91663 does not address the issue of providing a square wave form AC signal from a DC input signal.
Many applications require a more efficient waveform such as the aforementioned square waveform, wherein the wave travels directly from the maximum positive value to the maximum negative value of the alternating current, while remaining at each maximum value for approximately equal time intervals. While it is possible to achieve the square waveform with solid state electronic inversion circuitry, such circuitry would still be vulnerable to the aforementioned harsh environmental conditions.
Thus, a dc to ac power generator solving the aforementioned problems is desired.